Nothing unless your own personal experience from lots of shooting makes you feel like it is required. I really only have one that is a must, but it more for comfort.. Either a Magpul trigger guard or some other brand that fills the gap under the receiver that gives you the blister on your middle finger. It's kind embarrassing to give the RO the bird if he's telling you to stop shooting too so fast with a giant blister hanging out there.. Tactical Finger STD's are not cool..